A phase change memory (PCM) is a device which uses chalcogenide material as a memory element. A memory element is the element that stores information. A phase change memory stores information on a memory element by changing the phase of the element between amorphous and crystalline phases. Generally, the amorphous phase is associated with what is called a reset state and the crystalline state is associated with what is called a set state. Multilevel memories may have a number of states intermediate between set and reset states.
In the programming operation, a phase change memory may be transitioned through the application of bias voltages and resulting currents to transition from amorphous to crystalline states or from crystalline to amorphous states.
In some phase change memories, an ovonic threshold switch (OTS) is used as the select device. An integrated memory storage element (cell) of a PCM and an ovanic threshold switch is known as a PCMS. A high amount of power is generally used to write a PCMS. This power requirement limits the array bandwidth of a memory to, for example, 10-25 MByte/s.